According to hospital sources, the PTI leader's driver was also killed in the attack while his guard is said to be in a critical condition at the Combined Military Hospital (CMH).
Later Sunday, the Pakistani Taliban claimed responsibility for the suicide bombing that killed Gandapur.
There are also allegations that the intervention of the military establishment in the election process has been quite apparent - something that has paved the way for Imran Khan, the leader of Pakistan Tehreek-e-Insaf (PTI), to become the next Prime Minister of Pakistan.
In the three weeks leading to the vote, at least 179 people have been killed in attacks across the country, but mainly focused on the western Balochistan and Khyber Pakhtunkhwa provinces.
"We should give him a chance", said Muhammad Wasim, 32, pointing to what he described as the success Khan's party has had in governing northwestern Khyber-Pakhtunkhwa province.
On the other hand, several surveys carried out by national and worldwide organizations show PTI leading the political battle followed by Pakistan Muslim League Nawaz and Pakistan People's Party. He was elected through a by-election on the Dera Ismail Khan PK-67 seat, after it was vacated following the death of his brother Law Minister Israrulah Gandapur in a suicide attack.
Khan, who so far has had an "extended" election campaign across the country, has also dedicated most part of his speeches to attacking the Pakistan Muslim League-Nawaz (PML-N) and the Sharif family.
The PTI has accused India of supporting Nawaz Sharif and called it the main conspirator of the'international agenda against Pakistan
Recent polls show PTI's popularity climbing nationally.
"I am supporting Imran Khan because he is the best choice for Pakistan".
Whoever wins the election will need to seek an alliance with Bhutto's party or possibly a collection of independents.
It also postponed the balloting for the National Assembly seat from the garrison city of Rawalpindi, where a candidate from former prime minister Nawaz Sharif's party was disqualified after being convicted of substance abuse.
He entered politics in the late 1990s when memories of Pakistan's cricketers winning the World Cup were still fresh. No one can doubt your Honesty and thats what is require in our country...
BehindYouSkipper became one of the country's top trending hashtags as celebrities and former cricketers came to Khan's support.
He is the son of former prime minister Benazir Bhutto, who was assassinated in 2007.
Zimbabwe vs Pakistan 2018, Fifth ODI - Statistical Highlights
Their in-form openers - Fakhar Zaman and Imam-ul-Haq laid the foundation for a big total by adding 168 runs for the first wicket. Hosts Zimbabwe's misery ran along with the time as Pakistan ended the five match series with a complete white wash.